Highlights

Scientists have evidence indicating that the Gulf stream – the ocean current that gives Ireland its moderate climate – might be shifting North.

Ireland enjoys a moderate climate in large part because of the Gulf Stream, a warm current from the Gulf of Mexico which sweeps across the Atlantic, giving us the benefit of mild winters and temperate summers.

A collaboration between biologists from Canada and climatologists from Switzerland has discovered new evidence that the Gulf Stream, the warm current believed to be responsible for Ireland’s predominantly milder winters, has shifted north.

The study based off the coast of Nova Scotia on the east coast of Canada, traditionally home to the cold Labrador Current, analysed nitrogen isotopes found in cold water corals.

What is the evidence?

Scientists reached the startling conclusion when they plotted the nitrogen concentration in living coral. Fossil records can be used to provide data from coral from the distant past. The analysis is similar to using tree rings to measure growth rates over time.

The study bases its conclusions on a book written in 2003 by Dr Brian Fry of the University of Texas at Austin, who showed that nitrogen levels matched to different water sources. The warmer nutrient-rich Caribbean waters (the source of the Gulf Stream) have more living organisms. Hence the Gulf Stream has less Nitrogen-15 (a stable isotope) that the Labrador Current.

Historic levels of Nitrogen-15 (15N) in coral off the coast of Newfoundland have been relatively unchanged since around 600 AD at about 1.1%, the fossil record shows. But live specimens show a steady drop from this to less than 1% since the mid 1920s. That may not sound like much, but it is statistically significant, especially when you consider only 0.366% of all the nitrogen on the planet is Nitrogen-15.

A change in Nitrogen isotope concentration can come from the corals feeding different food, or the introduction of different nitrogen source into the food chain. The study suggests the Gulf Stream is the new nutrient rich source.

What does this mean for Ireland?

So does this mean December’s cold snap was caused by climate change affecting the Gulf Stream? Possibly, although the data plotted in Dr Owen Sherwood’s paper published in the Proceedings of the National Academy of Sciences only goes as far as the year 2000. The catastrophic suddenness of the recent cold snap also calls into question as to whether or not Ireland’s white Christmas in 2010 was caused by the diverted Gulf Stream. After all, winters haven’t been slowly getting colder and colder, we’ve just had two sudden cold snaps in a recent history marked by warm wet winters.

There may be a more complicated reason as to why the big freeze suddenly caught out so many in the Republic and the UK. Two possible reasons are a “tipping point” for the North Atlantic temperature or the eruption of the Icelandic volcano at Eyjafjallajökull last spring.

The scientists believe the change as evidence of anthropogenic climate change. Put simply, the Earth’s climate is changing and mankind is responsible. The statistics certainly correlate, although a relationship between the fossil records with known changes in temperature such as the European Medieval Warming Period or the Little Ice Age, would go a lot further towards statistical proof.

Dr Sherwood’s fossil record only has three data points; one around 600 AD and three more between 1700 and 1900, outside both of these climate phenomena. Despite these problems the paper is a powerful illustration of the importance of both interdisciplinary studies and the previously unpredicted relevance of corals in environmental archives.

One more important point raised by this study is the effect it may have on fishery stocks in the North Atlantic. If the nutrient rich Gulf Stream is being disrupted; then Ireland’s fishing industry, worth €380 million annually according to a 2002 OECD study, could be in further danger.

Notes

See science report at http://www.pnas.org/content/early/2010/12/27/1004904108.abstract

A note about identifying climate change impacts

Many events are linked to climate change by virtue of fitting a long-term trend. For example, the record-breaking “once in one thousand years” rains that drove the recent Nashville flood is part of the long-term trend of increasing heavy precipitation events in the Southeastern United States that has been fully documented and firmly attributed to climate change. While one cannot say with certainly that event was "caused" by climate change, one can and should say it is linked to climate change.